The present invention relates to a semiconductor device, and more particularly to a semiconductor device provided with both a high speed and a low power consumption.
FIG. 2 shows the prior art disclosed by JP-A-8-274620. (Hereinafter, this prior art will be denoted by the prior art A.)
An oscillation circuit OSC0 is constructed such that an oscillation frequency thereof changes in accordance with the value of a control signal received at a terminal B1 from a control circuit CNT0. The control circuit CNT0 is constructed such that it receives a reference clock signal CLK0 from the exterior and receives an oscillation output of the oscillation circuit OSC0. A closed circuit system composed of the frequency-variable oscillation circuit OSC0 and the control circuit CNT0 inputted with an output S0 of the frequency-variable oscillation circuit OSC0 is constructed to form a stable system in which each circuit is applied with a negative feedback. With this closed circuit system, the oscillation frequency of the output S0 of the frequency-variable oscillation circuit OSC0 assumes a frequency corresponding to the frequency of the reference clock signal CLK0. For example, the oscillation frequency of the output S0 is synchronous with or the same as the frequency of the external clock signal.
The oscillation circuit OSC0 is composed of an N-type MOSFET (NMOSFET) and a P-type MOSFET (PMOSFET) formed on a semiconductor substrate and a control voltage from the control circuit CNT0 changes the substrate bias of the MOSFET. With this construction, the threshold value of the MOSFET changes in accordance with the change in substrate bias so that the oscillation frequency of the oscillation circuit OSC0 changes.
Further, it is constructed that a main circuit LOG0 receives a control signal from the control circuit CNT0 at a terminal B0 and the control signal controls the substrate biases of MOSFET's forming the main circuit LOG0, thereby controlling the threshold voltage of the MOSFET.
With such a construction, it becomes possible to control the threshold voltage of the MOSFET in the main circuit LOG0 by the reference clock signal CLK0 so that the threshold voltage of the MOSFET forming the main circuit LOG0 and hence a power consumption and an operating speed are made variable in accordance with the frequency of the reference clock signal (or in accordance with an operating frequency).
In the prior art A, no limitation is imposed as to a method for distribution of the signal B0 to the MOSFET's in the main circuit LOG0. However, the method for distribution of the substrate bias to the main circuit has a large relation with the power consumption and the packaging density of the main circuit.
In the prior art A, the main circuit LOG0 is controlled by a signal at B0 corresponding to a signal at the terminal B1. This correspondence has a large relation with the stability of the substrate bias control circuit and the stability of the substrate bias voltage.
In order to solve the two problems mentioned above,
(1) the main circuit LOG0 in the prior art A is divided into a plurality of substrate control blocks by use of PMOS substrate bias switches and NMOS substrate bias switches, thereby making it possible to control the substrate bias of each circuit block independently of the substrate bias control circuit.
(2) In the embodiment of the prior art A, the signal B0 inputted to the main circuit LOG0 is a signal corresponding to the signal B1 inputted to the frequency-variable oscillation circuit OSC0. In an embodiment of the present invention, a substrate bias corresponding to the signal B0 is particularly generated by use of a substrate bias buffer from a substrate bias corresponding to the signal B1. An input impedance of the substrate bias buffer is made high and an output impedance thereof is made lower than the input impedance.
Next, description will be made of a cell layout suitable for construction of a semiconductor device provided with both a high speed and a low power consumption. The present invention relates to a semiconductor device and a cell library or a semiconductor device using the cell library, and more particularly to a semiconductor device in which a substrate bias and a supply voltage can be controlled independently of each other.
The layout of the conventional CMOS inverter is shown in FIG. 13. Symbol MP1 denotes a P-type MOS transistor (hereinafter referred to PMOS) composed of P-type diffused (or impurity) layers forming the source and drain of PMOS and a gate electrode, and symbol MN1 denotes an N-type MOS transistor (hereinafter referred to NMOS) composed of N-type diffusion (or impurity) layers forming the source and drain of NMOS and a gate electrode. Numeral 110 denotes a second metal layer which is supplied with a positive supply voltage (hereinafter referred to as VDD). Numeral 111 denotes a second metal layer which is supplied with a negative supply voltage (hereinafter referred to as VSS).
The substrate or well potential of the PMOS MP1 (hereinafter referred to as PMOS substrate or well bias) is supplied from a surface high-concentration N layer (hereinafter referred to as PMOS substrate or well diffused (or impurity) layer) 204. The PMOS substrate or well bias is connected to the second metal layer through a first metal layer 110 so that it is supplied with VDD. The substrate or well potential of the NMOS MN1 is supplied from a surface high-concentration P layer (hereinafter referred to as NMOS substrate or well diffused (or impurity) layer) 203. The NMOS substrate or well bias is connected to the second metal layer 111 through the first metal layer so that it is supplied with VSS. Thus, in the prior art shown in FIG. 13, the PMOS substrate or well bias is connected to VDD and the NMOS substrate or well bias is connected to VSS.
There is conventionally known a method in which a substrate or well bias is set to a potential different from a supply voltage in order to control the threshold value of a MOS transistor. In the cell structure shown in FIG. 13, however, it is not possible to set the substrate or well bias to a potential different from the supply voltage.
FIG. 14 shows the layout of a CMOS inverter cell in the case where it is constructed such that the substrate or well bias of a PMOS and the substrate or well bias of an NMOS can be set to a potential other than VDD and a potential other than VSS, respectively. The substrate or well bias of the PMOS is supplied from a second metal layer 112, and the substrate or well bias of the NMOS is supplied from a second metal layer 113. Since the second metal layers 112 and 113 are electrically isolated from second metal layers 110 and 111, respectively, the substrate or well bias of the PMOS and the substrate or well bias of the NMOS can be supplied with independent potentials.
Circuit diagrams corresponding to FIGS. 13 and 14 are shown in FIGS. 15A and 15B, respectively.
In the case where it is constructed such that the substrate or well bias of the PMOS and the substrate or well bias of the NMOS can be set to a potential other than VDD and a potential other than VSS, respectively, the following is apparent from the comparison of FIGS. 13 and 14.
(1) In the case where the height of a cell 300 is made the same as the height of a cell 200, the width of each of the power supply metal layers 110 and 111 becomes narrow. Thereby, a power supplying capability is deteriorated. (Hereinafter, this will be referred to as a first problem.)
(2) In the case where the power supply metal layers 110 and 111 of the cell 200 are made the same in width as the power supply metal layers 110 and 111 of the cell 200, the height of the cell 300 becomes higher than the height of the cell 200 because there is a wiring area for the second metal layers 112 and 113. Thereby, the area is increased. (Hereinafter, this will be referred to as a second problem.)
(3) In the case where a metal layer other than the second metal layer is used for the substrate or well bias supply lines 112 and 113, a restriction is imposed on a wiring in a cell and a wiring between cells. Thereby, the area is increased. (Hereinafter, this will be referred to as a third problem.)
In order to solve the first to third problems simultaneously, the supply of the substrate or well bias is performed by the PMOS substrate or well diffused (or impurity) layer and the NMOS substrate or well diffused (or impurity) layer. Alternatively, the supply of the substrate or well bias is performed by metal layers other than metal layers used for in-cell and inter-cell power supply wirings or signal wirings.
A method for power supply to each cell is known by, for example, JP-A-61-214448. In this known example, a contact is provided to a contact region for doped well and a well voltage supply is performed by the contact. In the present invention, there is no need to provide a contact for well voltage supply and the well voltage supply is performed through an impurity layer of an adjoining cell.
An example of a semiconductor integrated circuit device provided by the present invention comprises a logical circuit including a MIS transistor formed on a semiconductor substrate, a control circuit for controlling a threshold voltage of the MIS transistor forming the logical circuit, an oscillation circuit including a MIS transistor formed on the semiconductor substrate, the oscillation circuit being constructed so that the frequency of an oscillation output thereof can be made variable, and a buffer circuit, in which the control circuit is supplied with a clock signal having a predetermined frequency and the oscillation output of the oscillation circuit so that the control circuit compares the frequency of the oscillation output and the frequency of the clock signal to output a first control signal, the oscillation circuit is controlled by the first control signal so that the frequency of the oscillation output corresponds to the frequency of the clock signal, the control of the frequency of the oscillation output being performed in such a manner that the first control signal controls a threshold voltage of the MIS transistor forming the oscillation circuit, and the buffer circuit is constructed so that it is inputted with the first control signal to output a second control signal corresponding to the first control signal, the second control signal controlling the threshold voltage of the MIS transistor forming the logical circuit.
Also, bias switch circuits may be provided corresponding to the circuit blocks, respectively. The oscillation circuit is controlled by the first control signal so that the frequency of the oscillation output corresponds to the frequency of the clock signal, the control of the frequency of the oscillation output being performed in such a manner that the first control signal controls a threshold voltage of the MIS transistor forming the oscillation circuit, a second control signal corresponding to the first signal is inputted to the plurality of bias switch circuits which in turn outputs a plurality of third control signals, and the third control signals are inputted to the circuit blocks corresponding to the bias switch circuits which output the third control signals, the third control signals controlling a threshold voltage of the MIS transistor forming the circuit block.
Two control circuits including first and second control circuits may be provided. The first control circuit generates a control signal A so that the timing of rise of the oscillation output and the timing of rise of the clock signal coincide with each other. The second control circuit generates a control signal B so that the timing of fall of the oscillation output and the timing of fall of the clock signal coincide with each other. The oscillation circuit is controlled by the control signal A and the control signal B so that the oscillation output assumes the same signal as the clock signal, the control of the frequency of the oscillation output being performed in such a manner that the control signal A and the control signal B control a threshold voltage of the MIS transistor forming the oscillation circuit. At this time, the threshold voltage of the MIS transistor forming said logical circuit is controlled by a second control signal corresponding to a first control signal which includes the control signal A and the control signal B.
A cell layout in the circuit block comprises a first cell having at least one MIS transistor and a second cell having at least one MIS transistor, in which the first cell and the second cell are arranged so that they adjoin each other, the first cell is provided with a first impurity layer for supply of a substrate or well potential of the MIS transistor, the second cell is provided with a second impurity layer for supply of a substrate or well potential of the MIS transistor, and the first impurity layer and the second impurity layer are at least partially contiguous to each other so that the supply is made to the first impurity layer through the second impurity layer.
The substrate or well potential is supplied with a potential independent of a supply voltage. For example, the substrate or well bias is set so that a threshold value of the at least one MIS transistor becomes low when the semiconductor device is operating (or at the time of active condition) and the threshold value of the at least one MIS transistor becomes high when the semiconductor device is not operating (or at the time of standby). Also, the substrate or well potential may be set so that a threshold value of the at least one MIS transistor becomes high at the time of selection of the semiconductor device. Also, a power supply wiring may cover the impurity layer.
That the impurity layer is converted into a silicide, is preferable since a resistance thereof is small. A capacitance may be connected between the impurity layer which supplies the substrate or well potential and a power supply line.